Ink printing apparatuses can be used for single-color or multicolor printing to a printing substrate (for example a single sheet or a web-shaped recording medium) made of the most varied materials (paper, for example). The design of such ink printing apparatuses is known; see for example EP 0 788 882 B1. Ink printing apparatuses that operate according to the Drop on Demand (DoD) principle, for example, have as a printing unit a print head or multiple print heads with nozzles comprising ink channels, the activators of which nozzles—controlled by a print controller—exciting ink droplets in the direction of the printing substrate, which ink droplets are directed towards said printing substrate in order to apply print dots there for a print image. The activators can generate ink droplets thermally (bubble jet) or piezoelectrically.
Given low print utilization of the ink printing apparatus, in the printing process not all nozzles of the ink print heads are activated; many nozzles have downtimes (print pauses), with the consequence that the ink in the ink channel of these nozzles is not moved. Due to the effect of the evaporation out of the nozzle opening, the danger exists that the viscosity of the ink then changes. This has the result that the ink in the ink channel can no longer move optimally and exit from the nozzle, for example. In extreme cases, the ink in the ink channel dries up completely and blocks the ink channel, such that a printing with this nozzle is no longer possible.
The drying of the ink in the nozzles can be prevented in that printing takes place from all nozzles within a predetermined cycle. This cycle can be adjusted corresponding to the print utilization. Individual points can thereby be applied in unprinted regions of the printing substrate, or dotted print lines can be printed between print pages. These methods can lead to disruptions in the print image, in addition to unnecessary ink consumption and additional wear of the print heads.
These problems in particular occur in color printers. For example, here print bars with print heads are arranged in a fixed position relative to one another as a printing unit. For example, print bars with five respective print heads can be provided, respectively one print bar for the colors black, cyan, magenta, and yellow. Here the problem exists that one or more colors are not used, for example given black-and-white printing. Multiple cleaning cycles are then required in order to make the unused print heads current again.
From U.S. Pat. No. 6,578,945 B2, given an ink printing apparatus with multiple print heads it is known to avoid the drying out of the nozzles in that the nozzles are sealed with protective caps. Given cleaning, ink emitted from the nozzles is thereby captured by the protective caps. In order to apply the protective caps on the nozzles, the printing unit with the print heads is moved upward, away from the printing substrate; the protective caps are driven into the intervening space between the printing unit and the printing substrate. The print heads are thereby cleaned. The protective caps are moved upward onto the print heads via elastic force, wherein the print heads are covered. The protective cap unit remains in this position until the printing unit should be used for printing again.
In US 2007/0157962 A1, an ink printing apparatus is described in which the print head can be moved vertically upward from the printing substrate, between a printing position and a position in which no printing is conducted. In this printing position, a protective cap made of rubber can be applied onto the nozzles of the print head.
From DE 10 2005 034 029 A1, an ink printing apparatus is known with multiple print heads arranged serially in the transport path of the printing substrate. The ink print heads serially print a resulting print image onto the printing substrate. Individual ink print heads can be deactivated and shifted to the side, for example in order to service these while the remaining print heads can continue to print.
DE 197 26 642 C1 describes a device for positioning an ink print head and a cleaning and sealing device. The ink print head can be swung from a printing position into a cleaning position and back again. A cleaning and sealing device can be displaced into the ink print head and away from this again. The cleaning and sealing device has a sealing cap and a wiping lip.